qml and c++ with qt quick 2 application

Question

I have a qml GUI of my main window. I just created a qt quick2 application and copied and pasted qml GUI of my main window to main.qml. When I run the application, it displays blank window and following is my qml log:

    QML debugging is enabled. Only use this in a safe environment.
Both point size and pixel size set. Using pixel size. 
Both point size and pixel size set. Using pixel size. 
Both point size and pixel size set. Using pixel size. 
file:///home/khajvah/build-convQML-Desktop_Qt_5_1_0_GCC_64bit-Debug/qml/convQML/main.qml:99:9: QML Text: Cannot anchor to an item that isn't a parent or sibling.
file:///home/khajvah/build-convQML-Desktop_Qt_5_1_0_GCC_64bit-Debug/qml/convQML/main.qml:31:9: QML BasicButton: Cannot anchor to an item that isn't a parent or sibling.
file:///home/khajvah/Qt5.1.0/5.1.0/gcc_64/qml/QtQuick/Controls/Styles/Base/ToolButtonStyle.qml:73:9: QML Image: Cannot open: file:///home/khajvah/build-convQML-Desktop_Qt_5_1_0_GCC_64bit-Debug/logout-512.png
file:///home/khajvah/Qt5.1.0/5.1.0/gcc_64/qml/QtQuick/Controls/Styles/Base/ToolButtonStyle.qml:73:9: QML Image: Cannot open: file:///home/khajvah/build-convQML-Desktop_Qt_5_1_0_GCC_64bit-Debug/console.ico
file:///home/khajvah/Qt5.1.0/5.1.0/gcc_64/qml/QtQuick/Controls/Styles/Base/ToolButtonStyle.qml:73:9: QML Image: Cannot open: file:///home/khajvah/build-convQML-Desktop_Qt_5_1_0_GCC_64bit-Debug/mod.png
QQuickView only supports loading of root objects that derive from QQuickItem. 

If your example is using QML 2, (such as qmlscene) and the .qml file you 
loaded has 'import QtQuick 1.0' or 'import Qt 4.7', this error will occur. 

To load files with 'import QtQuick 1.0' or 'import Qt 4.7', use the 
QDeclarativeView class in the Qt Quick 1 module. 

the following is my qml file:

import QtQuick 2.1
import QtQuick.Controls 1.0
import QtQuick.Window 2.0

ApplicationWindow {
    id: applicationwindow1
    title: qsTr("Converter")
    width: 500

    //height: 600




//    menuBar: MenuBar {

  //  }

    ToolBar {

        id: tool_bars
        x: 0
        y: 0
        width: applicationwindow1.width
        height: 39
        clip: true
        smooth: false
        opacity: 1
        transformOrigin: Item.Center

        ToolButton {

            id: modify

            y: 1
            scale: 1
            anchors.right: tool_bars.left

            iconSource: "../../mod.png"

        }

        ToolButton {

            id: consolebtn
            x: 32
            y: 1
            scale: 1
            anchors.left: modify.right
            anchors.leftMargin: 6
            iconSource: "../../console.ico"


        }


        ToolButton {

            id: exit;
            x: 75
            y: 1
            scale: 1
            anchors.left: consolebtn.right;
            anchors.leftMargin: 6

            iconSource: "../../logout-512.png"

        }

    }

    GroupBox {
        id: group_box1
        x: 0
        y: 30
        width: 500
        height: 136
        anchors.top: tool_bars.bottom
        anchors.topMargin: -9
        anchors.left: parent.left
        anchors.leftMargin: 0
        anchors.right: parent.right
        anchors.rightMargin: 0

        ComboBox {
            id: typebox



            anchors.left: text1.right
            anchors.leftMargin: 5

            width: 70
            height: 23
            anchors.top: parent.top
            anchors.topMargin: 37
        }

        Text {
            id: text1

            anchors.left: group_box1.left
            anchors.leftMargin: 5

            text: "Type:"
            anchors.top: parent.top
            anchors.topMargin: 41
            font.italic: true
            style: Text.Normal
            font.pointSize: 12
            font.pixelSize: 12
        }


        ComboBox {

            id: frombox
            x: 205


            anchors.left: text2.right
            anchors.leftMargin: 8

            width: 70
            height: 23
            anchors.top: parent.top
            anchors.topMargin: 37
        }

        Text {
            id: text2
            x: 189


            anchors.leftMargin: 20

            text: "From:"
            anchors.top: parent.top
            anchors.topMargin: 41
            anchors.horizontalCenterOffset: -32
            anchors.horizontalCenter: parent.horizontalCenter
            font.italic: true
            style: Text.Normal
            font.pointSize: 12
            font.pixelSize: 12
        }


        ComboBox {
            id: tobox
            x: 412


            anchors.right: parent.right
            anchors.rightMargin: 5

            width: 70
            height: 23
            anchors.top: parent.top
            anchors.topMargin: 37
        }

        Text {
            id: text3
            x: 0


            text: "To:"
            anchors.top: parent.top
            anchors.topMargin: 41
            anchors.right: tobox.left
            anchors.rightMargin: 5
            font.italic: true
            style: Text.Normal
            font.pointSize: 12
            font.pixelSize: 12
        }

        TextField {
            id: text_field1
            y: 78
            width: 197
            height: 22
            anchors.bottom: parent.bottom
            anchors.bottomMargin: 15
            anchors.left: parent.left
            anchors.leftMargin: 5
            placeholderText: "Input"
        }

        TextField {
            id: text_field2
            x: 293
            y: 78
            width: 186
            height: 22
            anchors.bottom: parent.bottom
            anchors.bottomMargin: 15
            anchors.right: parent.right
            anchors.rightMargin: 5
            readOnly: true
            placeholderText: "Result"
        }


    }

    TextArea {
        id: text_area1
        x: 0
        y: 178
        width: 500
        height: 80
        anchors.left: parent.left
        anchors.leftMargin: 0
        anchors.right: parent.right
        anchors.rightMargin: 0
        anchors.top: group_box1.bottom
        anchors.topMargin: 12
        anchors.bottom: addlogbtn.top
        anchors.bottomMargin: 5
    }

    Button {

        id: addlogbtn
        x: 7
        y: 212
        width: 110
        height: 23
        text: "Add to Log"

        anchors.bottom: parent.bottom
        anchors.bottomMargin: 5
        anchors.left: parent.left
        anchors.leftMargin: 7


    }

    Button {
        id: button1
        x: 195
        y: 212
        width: 118
        height: 23
        text: "Export"
        anchors.horizontalCenter: parent.horizontalCenter
        anchors.bottom: parent.bottom
        anchors.bottomMargin: 5
    }

    Button {
        id: button2
        x: 359
        y: 212
        width: 117
        height: 23
        text: "Clear"
        anchors.right: parent.right
        anchors.rightMargin: 7
        anchors.bottom: parent.bottom
        anchors.bottomMargin: 5
    }


}

and automatically generated main.cpp:

#include <QtGui/QGuiApplication>
#include "qtquick2applicationviewer.h"

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QtQuick2ApplicationViewer viewer;
    viewer.setMainQmlFile(QStringLiteral("qml/convQML/main.qml"));
    viewer.showExpanded();

    return app.exec();
}

Any ideas why this does not work? I am new to qml and I am really confused how it is connected to c++.

Solution

You can definitely use ApplicationWindow, but you need to use QQmlApplicationEngine, and you need to explicitly show your toplevel window. You can see a complete example in another answer. Below is just a main.cpp file that should work for you.

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQuickWindow>

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;
    engine.load(QUrl("qml/convQML/main.qml"));
    QObject *topLevel = engine.rootObjects().value(0);
    QQuickWindow *window = qobject_cast<QQuickWindow *>(topLevel);
    window->show();
    return app.exec();
}